1. Technical Field
The present invention generally relates to a software algorithm for controlling the engine of a motor vehicle. More particularly, but without restriction to the specific embodiment and/or use which is shown and described for purposes of illustration, the present invention pertains to a fuel identifier algorithm capable of distinguishing the difference between normal fuel and high driveability index fuel.
2. Discussion
In recent years, the manufacturers of internal combustion engine fuel have began to offer a variety of different fuels having vaporization pressures to correspond with the climate in which they are sold. For example, fuels exhibiting a Reid vaporization pressure of approximately 7-9 psi are commonly sold in the warmer climate regions of the country or only during the summer. Similarly, fuels exhibiting Reid vaporization pressures of 12-14 psi are utilized primarily in the winter. By varying the vaporization pressure to correspond to the average daily temperature, the cold start characteristics of the internal combustion engine may be optimized.
One of the specific problems attempted to be solved by varying the vapor pressure of the fuel is a warm weather phenomenon known as vapor lock. If the ambient temperature is high and the fuel volatility or vapor pressure is also high, the fuel may vaporize on its way to the fuel injection system. Accordingly, the fuel will not pump and the engine will stall due to lack of fuel. Conversely, a different concern exists during cold weather. For example, an engine may fail to start during a cold weather snap if a fuel exhibiting a high driveability index or low vapor pressure is used. Specifically, the fuel may simply wet the walls of the cylinder without vaporizing thereby precluding combustion. Accordingly, the engine will not start and the fuel will be pumped through the combustion chambers and into the exhaust.
With the advent of the use of high driveability index fuel, engine control systems face a new challenge. Specifically, accommodations must be made to assure that the engine will start easily and meet strict emission standards regardless of ambient temperature or fuel type. This goal is more complex since fuels of high driveability index may be in the tanks of vehicles during a seasonal change or a cold snap. As emission standards are tightened, it becomes increasingly difficult to meet both the emission standard and an acceptable level of driveability robustness as determined by the customer. Accordingly, a need exists for a method to identify when high driveability index fuel is present and modify the enrichment/control strategy to compensate for the fuel's lower volatility.
In the past, systems commonly known in the art would simply enrich the mixture at start for all fuels in an attempt to assure an easy start. However, this strategy is no longer viable when evaluated using the emission standards of today. One of the greatest hurdles facing original equipment manufacturers is that the vehicle must meet not only a new car emission standard but must also pass an audit performed up to three years after the initial sale. Recently developed systems have attempted to assure that the emission standards were met over time by setting the initial enrichment to a goal maximum roughness setting equivalent to the most lean setting acceptable. This control strategy would allow the emissions level to increase over time as the engine components wear. However, if a fuel of lesser volatility were used, the engine would be pushed into roughness thereby dissatisfying the operator.